Treatment of viscose



Patented Nov. 1, 1949 TREATMENT OF VISCOSE Russell Owens Denyes, Rome, Ga., assignor, by mesne assignments to Celanese Corporation of America, a corporation of Delaware No Drawing. Application February 1,1946, Serial No. 645,016

1 Claim.

This invention relates to. the purification of freshly formed viscose products and has for its object the preparation of such products with extremely low mineral content as'refi'ected by combustion. tests in which the material is reduced to ash.

Freshly regenerated. viscose products, such as rayon, cellophane, artificial sausage casings and staple fiber contain adherent and occluded. acid picked up during their passage through the conventional regeneratingbath, together with appreciable amounts of reaction products. These require removal in a process known as purification. Purification generally comprises a sequence of aqueous treatments. purification comprises such steps as washing with plain or alkalinized warm water to remove the adherent and occluded acid and water soluble salts and to distill out the occluded carbon disulfide, treating with a sulfur solvent such as an aqueous solution of sodium sulfide, ammonium sulfide or sodium hydroxide, and finally rinsing with lukewarm water. The product is then dried. In some processes, this sequence may be altered. Thus, in the viscose rayon pot spinning art, the rayon is sometimes dried after the initial acidremoval treatment, and then subsequently rewetted, desulfurized, rinsed and redried.

It is known that when ordinary tap water is used for the purification of regenerated cellulose products, the evaporation of the water during drying results in a deposition of calcium and magnesium salts on the product. In the case of purifying rayon in package form, such as spin bobbins, cakes or skeins, the salts tend to migrate by capillary action or wicking from the inner parts of the package and concentrate on the outer surfaces thereof. The presence of these salts is deleterious because it manifests itself as chalky streaks, because the portions afilicted with deposits do not take up dyestuffs uniformly with respect to the remainder of the yarn, and because the salt deposits cause a degradation of the yarn which is reflected in markedly reduced tensile strength.

To minimize these deleterious effects resulting from the use of ordinary tap water, studies have been made of the use of water which had been chemically softened, for example, by passage through a bed of sodium zeolite. By this technique sodium salts rather than calcium and magnesium salts are deposited by the water as it evaporates. However, such treatment was found to result in no significant improvement in chalkiness.

It is also known that cellulosic material is capable of undergoing base-exchange reactions; and that at a relatively low pH value, i. e., below approximately pH 2.5, the carboxyl groups are free of any combination with metallic ions. In

The viscose production the viscose process, the regenerated cellulose products leaving the regenerating bath have few,

if any metallic ions chemically combined with the cellulosic matter because of the high degree of acidity. However, as the acidity is reduced during the rinsing operation, there is theoretically a progressively increasing combination between the cellulose and any cations other than the hydrogen ion that may be present in the liquid, such as the ions of sodium, calcium and magnesium.

My invention provides improvements in the viscose process which effectively diminish the salts which migrate to the surface and the metallic cations which combinewith the cellulose, as in the present practices just described. Through experiments I have confirmed my discovery that it is entirely feasible, ina. commercial or economic sense, to "produce viscose products which are practically mineral-free, i. e., of, ex.- tremely low ash content, by employing demineralized water in the rinsing operations in combination with an aqueous solution of a metallic-element-free sulfur solvent, such as ammonium sulfide as the desulfurizing agent. I

have found that such metallic-element-free products have properties superior to comparable products now produced.

Moreover, I have discovered that it is not necessary to employ demineralized water from the very beginning to the end of the purification operation and that ordinary tap water, containing the usual moderate content of calcium and magnesium salts, or sodium-zeolite softened water, may be used for efiecting the rinsing out of the adherent regenerating bath if the desulfurizing solution comprises ammonium sulfide or the like in demineralized water, and demineralized water is used for effecting all of the rinses subsequent to the desulfurizing treatment.

My invention, accordingly, provides an improved method for the purification of viscose products by desulfurizing with a solution of ammonium sulfide in demineralized water and using demineralized water for all subsequent rinsing. Advantageously my invention comprises the use of ordinary tap water (not demineralized) for the removal of acid and salts, followed by desulfurizing with an ammonium sulfide solution in demineralized water and rinsing with demineralized water. As used herein, the term demineralized water refers to water that is wholly or substantially mineral-free, such as distilled water or water prepared through ion-exchange resins.

My invention will be understood by consideration of the following illustrative example. Although this example is presented in terms of the purification of viscose rayon produced by the bobbin spinning process, it will be' appreciated by those conversant with the art that the principles involved are equally applicable in the analogous manufactures of viscose staple fiber, viscose rayon produced by the pot spinning process, viscose rayon produced by continuous spinning processes, viscose artificial sponge, cellophane, artificial sausage casings and the like.

Example Spin bobbins of 150 denier, 40-filament viscose rayon were subjected variously to the following purification schedules, in which the times of the several treatments are given in minutes. spin bobbin represented approximately one pound of finished, dried and moisture-regained rayon. The bobbins were purified in a conventional vacuum-purification apparatus, the vacuum applied to the interior of the bobbins being such as to produce an average flow rate of 0.01 gallon per minute through the package.

Schedules 50 11W 150 HW 5o HW so HW 5o HDMW 200 HW 200 HW 200 HW 200 HW 200 HDMW 100 HW 100 HW 100 HW 100 HW 100 HDMW 100 s 100 s 100 s 100 SDMW o SDMW 2o HW 2o HW 2o CDMW CDMW 20 GDMW so HW so oDMW so oDMw so ODMW so ODMW Total ash, percent o. 150 o. 077 o. 061 o. 009 o. 011

HW-Hot (50 0.) hard water.

S-Ammonium sulfide (0.4%) in hard water.

HDMW-Hot (50 C.) distilled or demineralized water. ODMWCold (-30 C.) distilled 0r demineralized water.

SDMW-Ammonium sulfide (0.4%) in distilled or demineralized water.

Each

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,907,101 Funcke May 2, 1933 FOREIGN PATENTS Number Country Date 495,056 Great Britain Nov. '7, 1938 OTHER REFERENCES Journal of the Textile Institute, vol. 24, pp. T-123-T-144, Artificial Silk and its Manufacture, by Foltzer 1926, pp. 68-75. (Copy in Div. 15.) 

